Fodor’s target was, essentially, the logical positivist idea (still exceedingly common among scientists, despite the philosophical demise of logical positivism a number of decades ago) that the natural sciences form a hierarchy of fields and theories that are (potentially) reducible to each next level, forming a chain of reduction that ends up with fundamental physics at the bottom. So, for instance, sociology should be reducible to psychology, which in turn collapses into biology, the latter into chemistry, and then we are almost there.

But what does “reducing” mean, anyway?

He mostly complains about reductionism as believed by most scientists, and expressed in extreme form by Steven Weinberg.

The main gripe is that scientists usually feel that they are part of a collective enterprise that is systematically progressing towards the true workings of the universe, as part of one coherent methodology called science. But academic philosophers have all concluded decades ago that there is no such thing as scientific truth, that science does not make progress, that scientists jump on paradigms like fads, that science is a huge hodge-podge of contradictory theories, and that even within a subject like physics, science is just a bunch of loosely-related ideas that have little to do with each other. Scientists are just not self-aware enuf to see what they are doing.

When you discover that most scientists subscribe to a philosophy that all philosophers reject, that should be a clue that the philosophers are on the wrong track.

This is why scientists ignore modern philosophers: the philosophers are crackpots, and are so completely wrong it is hard to explain why they are so wrong. The simplest way to see it is that scientists accomplish things, and philosophers have zero influence on science or anything else.

It is perhaps only a slight exaggeration to say that scientific realism is characterized differently by every author who discusses it, and this presents a challenge to anyone hoping to learn what it is.

So nobody knows what realism means, and yet its virtue is one of philosophy's clearest debates.

Richard, yeah, it’s not just a slight exaggeration, it’s a pretty serious misrepresentation of the situation. A recent survey of a number of opinions of philosophers, co-authored by David Chlamers, clearly pointed to realism having won the day, especially within the epistemically relevant community, philosophers of science.

Yes, the big majority said that they favor scientific realism, but the survey did not define it or establish that there was a common definition. These philosophers can babble for 100s of pages on the subject, but never clarify their terminology enuf to say who was the realist and anti-realist in the Bohr-Einstein debates. The whole subject has the flavor of people who have never heard of XX-century science.

Several years ago I would have said that of course I was a scientific realist. But then I learned that when the term is applied to quantum mechanics, it usually means people like Einstein, Bohm, and Bell who believe that some hidden variable theory was going to disprove quantum mechanics. I do not know how "realism" came to mean a mystical belief that have never been seen or found any useful application to the real world, but because of that, put me down as an anti-realist, and the philosophers as being hopelessly confused.

Crazy as all that is, here is where Pigliucci really goes off the deep end:

Ah, yes, causality! I stayed away from that one too, partly because I’m thinking of a separate essay about it. The interesting thing is that the concept of causality plays an irreplaceable role in the special sciences, but hardly appears at all in fundamental physics. That’s something to explain, of course, and I’d like to hear a physicist’s opinion of it.

I responded:

I am baffled by this comment, as causality is absolutely central to fundamental physics. I cannot think of any part of physics that can function without it. Saying that causality does not appear in physics is like saying energy does not appear in physics. What is physics without energy and causality?

Perhaps you have been influenced by some misguided philosopher like Bertrand Russell. He wrote a 1913 essay saying that “the law of causality, as usually stated by philosophers, is false, and is not employed in science.” He also said that physics never even seeks causes. I do not know how he could say anything so silly, as all the physics textbooks use causality.

Vojinovic: “notion of causality is related to the notion of determinism”

Not really. There are people who work on deterministic and non-causal interpretations of quantum mechanics, and non-deterministic and causal interpretations. So they are not so tightly related.

I also disagree with your claim that radioactive decay is causeless, and that a causal chain of events makes no sense with quantum phenomena. The atomic nucleus consists of oscillating quarks and gluons, and the decay might be predictable if we could get a wave function for everything in that nucleus. That seems impossible, but there is still a causal theory for how that decay takes place, and the decay can be analyzed as a causal chain of events. Saying that radioactive decay is causeless is like saying a coin toss is causeless. It may seem like it has a random outcome to the casual observer, but there are causal explanations for everything involved.

Quantum mechanics is all about finding causal explanations for things like discrete atomic spectra, where such an explanation must have seemed impossible.

Yes, there are philosophers of physics today who work on those non-causal interpretations. As far as I know, nothing worthwhile has ever come out of that work.

Pigliucci posted this response:

No, it is your comment that is one more example of groundless condescending while refusing to engage with the actual argument in a way that may persuade others to actually take you seriously. ...

I’m afraid you either don’t get what Cartwright is saying or you don’t understand physics. Or possibly both. ...

It isn’t a question of what type of causality, it is an issue of causality period. According to my understanding of fundamental physics (and yes, I did check this with several physicists, Sean Carroll among them) the concept of causality plays little or no role at that level of description / explanation. Quantum mechanical phenomena “occur” with this or that probability, following the predictions of a set of deterministic equation, but one doesn’t need to deploy talk of causality at all.

On the contrary, one simply can’t do anything in the special sciences without bringing up causes. This is true for non fundamental physics, chemistry, biology (especially ecology and evolutionary biology), and so forth.

I realize how people can disagree with me on quantum computing, and even free will. But I really do not see how anyone can deny that causality is central to physics.

If I really misunderstand physics that badly, maybe I should shut down this blog. Can someone please give me some example of some part of physics that does not involve causality?

The only example given was radioactive decay, but you can find causal explanations from modern quantum field theory on the Wikipedia page. Someone claimed that there are no causal chains in quantum mechanics, but Feynman diagrams do exactly that.

It is true that physics textbooks do not use the word "causality" a lot. Instead of "A causes B", they might say "solving the equations of motion with initial conditions A gives B" or "A is the Cauchy data for B". Instead of saying "A has no causal effect on B" they might say "B is outside the light cone of A" or "A and B are are space-like separated".

It doesn't matter whether the theory is deterministic or not. Even if you are using a wave function to predict a probability, you still have to solve an initial value problem for the Schroedinger equation, which means that a wave function at one time is causing a wave function at future times. When explaining a laser, you still say that it is causing electrons to jump to excited states, and then causing emission of coherent photons.

Causality is so important in quantum field theory that it is one of the four Wightman axioms for such theories.

At the cosmological scale, physicists are always talking about things like what causes supernovas, even if they have never predicted one.

Why would someone think that causality is important in chemistry, but not fundamental physics? I am really trying to understand how someone could be so wrongheaded. What do they think physics is all about, if not causality?

Please tell me if I am wrong about causality. If so, I might have to post a correction, like Scott or Neil.

1 comment:

The biologist has got it wrong. He must have misunderstood what Prof Carroll said to him.

Admittedly, the uncertainty principle and Copenhagen notion of intrinsically probabilistic are confusing.

But even if, for example, a radioactive decay were entirely random (which I for one doubt) what about the consequences of that decay.

Prof Carroll could perhaps have explained to Prof Pigliucchi that even in the Copenhagen approach, it is assumed that in the unobserved Schrodinger phase, that occurs before and until measurement, and must therefore account for 90 .99 something per cent of what is happening in the Universe, everything proceeds deterministically.

He could have also mentioned conservation, Noether's theorem and local gauge theories all of which seem to point to a mysteriously deterministic world underlying quantum mechanics.

Perhaps the popular science press has something to answer for here. It likes to talk about dead and alive cats and many worlds.